The present invention relates in general to a method of producing a seat pad structure, and more particularly, to a method of producing a frame-installed seat pad structure which generally comprises a rectangularly extending frame, springs extending between opposed portions of the frame and a foamed plastic cushion pad mounted on the frame and the springs. More specifically, the present invention is concerned with a method of distributing a foamable plastic material evenly throughout a cavity of a mold.
2. Description of the Prior Art
Hitherto, a so-called "monobloc molding method" has been widely used particularly in the field of seat cushion manufacturing.
That is, in order to produce a frame-installed seat pad structure, the method carries out a process which comprises putting a frame in a cavity of a mold, putting a lid on the mold to close the cavity, fastening the lid to the mold, pouring a foamable plastic material into the cavity through an inlet opening formed in the lid, and curing the material under a given condition.
However, this method has the following drawback due to its inherency.
That is, during pouring of the material into the mold through the single inlet opening of the lid, it tends to occur that the material gathers at a certain position near the inlet opening and foaming starts from the material lump at the position and advances outwardly therefrom. This phenomenon however causes not only formation of undesired air-pockets in the foamed product but also undesired underfill at the peripheral portion of the product.